As part of the process of maturation of the initial contact of nerve and muscle into a functioning synapse, the nerve must start to release transmitter onto the muscle cell, and in addition, the nerve-muscle contact must be stable and continue to release transmitter. The experiments of this project will focus on these two important areas of synaptic development: What are process(es) which initiate the start of transmitter release at early nerve-target contacts? What mechanisms contribute to the stability of this release? Specifically, the project will examine the role of cell surface molecules and as well as diffusible substances in the starting of transmitter release in newly contacted nerve-muscle cell pairs. In addition, the project will investigate the participation of gap junctions in the stabilization of the new synapse. Lastly, the project will examine the development of transmitter release at neuronal soma-muscle contacts. Cultured nerve and muscle cells of the frog Xenopus laevis will be used in combination with the patch clamp technique in order to achieve a high level of control over the geometry and resolution of the measured transmitter release from nerve to muscle. The long term objective of these experiments is to enhance the understanding of the initiation and stabilization of transmitter release at developing synapses, in order to shed light on defective developmental growth, and possibly in degenerative diseases of the neuromuscular system.